This invention relates to the use of zinc-containing compositions for pharmaceutical and cosmeceutical purposes.
Zinc is one of the most important trace elements in human health and nutrition and plays a significant role in the function of many intracellular proteins. Zinc is crucial for gene expression and nucleic acid metabolism, which accounts in part for its importance in cellular growth and differentiation. Recent investigations indicate that zinc may actually have a regulatory role. Zinc possesses ligand-binding properties that are utilized effectively at the catalytic site of a broad range of enzymes. In addition, it has many structural roles in biological membranes [Tang et al., (2001) J Nutr 131: 1414-14200], cell receptors, and proteins (i.e. transcription factors and proteins involved in DNA replication). Zinc has been shown to have an effect on epidermal growth factor (EGF)-stimulated intracellular signaling [Wu et al., (1999) Am J Physiol 277: L924-L931] and numerous studies also indicate that zinc possesses insulin-like effects [Tang et al., supra]. Zinc has also been shown to cause an increase in IGF-I and TGF-beta 1 in femoral-diaphyseal and metaphyseal tissue cultures [Ma et al. (2001) Int J Mol Med 8(6): 623-8].
Studies have shown that zinc has an effect on epidermal growth factor (EGF) stimulated signaling. Addition of 0.3 mM of zinc or epidermal growth factor resulted in a marked increase in tyrosine phosphorylation of proteins in whole cell extracts [Hansson et al. (1996) Arch Biochem and Biophys 328 (2): 233-238]. Zinc has been found to be a potent inhibitor of protein tyrosine phosphatase (PTPase) [Wang et al. (1992) J Biol Chem 267(23): 16696-16702], which may induce increased protein tyrosine phosphorylation and generate activation of a host of intracellular signaling that includes MAP kinase activity [Hansson et al., supra]. A wide range of integrated biological responses has been associated with EGFR signaling. These biological responses include mitogenesis, apoptosis, enhanced cell motility, protein secretion, and differentiation or dedifferentiation even on the same cell, depending on the phenotype [Wells (1999) EGF receptor. Int J Biochem Cell Biol 31(6): 637-643]. EGFR signaling in adult animals has been postulated to play a role in organ repair and experimental results indicate that EGFR inhibition affects epithelial cell proliferation and stratification. Furthermore, EGFR may also affect wound healing and play a role in maintaining normal epithelial thickness [Nakamura et al. (2001) Exp Eye Res 72(5): 511-517]. In a number of patents and publications, zinc has been implicated to play a role in increasing wound healing, and the EGFR signaling pathway may be a key to its ability to help repair wounds.
Zinc has the potential to exert insulin-like effects with respect to lipogenesis [Coulston et al. (1980) Diabetes 29(8): 665-667], glucose transport and glucose oxidation in rat epididymal adipocytes [Shisheva et al. (1992) Diabetes 41(8): 982-988; May et al. (1982) J Biol Chem 257(8): 4362-4368]. Moreover, zinc also potentiates the mitogenic signaling of insulin [Kiss et al. (1997) FEBS Lett 415(1): 71-74]. Evidence points out that zinc may actually be involved in several steps of the insulin-signaling pathway. Zinc has been reported to exert positive effects on insulin synthesis and secretion and also is required for structural conformation of insulin [Chausmer et al. J Am Coll Nutr 17: 109-115]. In adipocytes, zinc has been shown to stimulate insulin-specific binding through an unknown mechanism [Gomot et al. (1992) Biol Trace Elem Res 32: 331-335; Herington (1985) Horm Metab Res 17: 328-332]. As mentioned above, zinc also possesses the ability to inhibit PTPase activity. PTPase is an early and critical juncture in insulin signaling. Membrane-associated PTPase activity antagonizes the effects of the insulin receptor and other growth factor-associated tyrosine kinases [Kremerskothen et al. (1993) Mol Cell Biochem 125: 1-9; Li et al. (1997) Endocrinology 138: 2274-2279; Samet et al. (1999) Am J Respir Cell Mol Biol 21: 357-364]. There are several branch points in the insulin-signaling pathway. One of these branch points involves the activation of phosphatidylinositol 3-kinase (PI 3- kinase). PI 3-K is well known to be necessary for the recruitment of GLUT4 to the cell surface. Specific isoforms of protein kinase C (PKC) appear to be necessary for the redistribution of GLUT 4 from intracellular storage sites to the plasma membrane [Braiman et al. (1999) Mol Endocrinol 13: 2002-2012; Kanoh et al. (2000) J Biol Chem 275: 16690-16696; Standaert et al. (1999) J Biol Chem 274: 25308-25316.]. PKC membrane localization and activity can be stimulated by zinc [Csermely et al. (1988) J Biol Chem 263: 6487-6490; Forbes et al. (1990) Biochem Int 22: 741-748; Forbes et al. (1990) Biochim Biophys Acta 1053: 113-117; Quest et al. (1992) J Biol Chem 267: 10193-10197]. Recent evidence has shown that zinc may regulate the Ser/Thr protein kinase termed mammalian target of rapamycin or mTOR (also known as FRAP and RAFT) [Lynch et al. (2001) Am J Physiol Endocrinol Metab 281(1): E25-E34]. The mTOR signaling pathway begins at the PI 3- kinase activation site. A downstream target of the mTOR pathway is the 40 S ribosomal protein S6, which is a substrate of p70S6k [Lynch, supra]. Amino acids increase mRNA translation (independently of merely serving as substrates for synthesis) through ribosomal protein S6 kinase [Patti et al. (1998) J Clin Invest 101(7): 1519-1529]. The 70 kDa ribosomal S6 kinase (p70S6K) is an important regulator of cellular translational capacity due to its ability to phosphorylate the 40 S ribosomal protein S6 and regulate 5′-terminal oligopyrimidine tract mRNAs [Martin et al. (2001) J Biol Chem 276(11): 7884-7791]. The activation of ribosomal protein S6 therefore up-regulates ribosome biosynthesis and enhances the translational capacity of the cell. Additionally, ribosomal protein S6 has been implicated in the regulation of cell size [Martin et al., supra].
Insulin-like growth factor-I (IGF-I) and transforming growth factor beta-1 (TGF-β1) play important roles in the biological system. The effect of zinc on IGF-I and TGF-β1 production was investigated to determine the role of this metal on growth of growth in newborn rats [Ma, supra]. The results of the experiments showed that the presence of zinc caused a significant increase in protein, IGF-I and TGFβ1 concentrations in medium cultured with diaphyseal or metaphyseal tissues. In addition, expression levels of IGF-I and TGF-β1 were also significantly increased in the diaphyseal and metaphyseal tissues cultured with zinc. Transforming growth factor betas are multifunctional polypeptide growth factors that are involved in proliferation and differentiation of cells, embryonic development, wound healing and angiogenesis [Blobe et al. (2000) N Engl J Med 342(18): 1350-1358]. Usually, TGF-beta1 is bound to the extracellular matrix, and can be released by proteases [Taipale et al. (1992) J Biol Chem 267: 25378-25384]. The presence of extracellular matrix has been found to down regulate the expression of the TGF-beta1 gene [Streuli et al. (1993) J Cell Biol 120: 253-260]. Therefore, TGF-beta may act as a feedback regulator of extracellular matrix formation. TGF-β regulates cellular processes through binding to high-affinity membrane receptors, which causes the assembly of a receptor complex that phosphorylates the proteins of the SMAD family [Blobe et al., supra]. SMADs act as signal transducers of TGF-β family members. After phosphorylation, SMADs form a complex and move into the nucleus and assemble complexes that directly control gene expression through DNA binding and recruitment of transcriptional co-activators or co-repressors [Massague J. (2000) Nat Rev Mol Cell Biol 1(3): 169-178]. SMADs help to regulate a number of genes including those for collagen [Zhang et al. (2000) J Biol Chem 275(50): 39237-39245] and regulation of SMADs is achieved in several different ways. Once in the nucleus, the activated SMAD complex may activate or repress gene expression. SMADs may bind to p300 (co-activator) or TG3-interacting factor (TGIF) (co-repressor) depending on their relative levels in a cell [Massague, supra]. Evidence suggests that TGIF may set the maximal level to which TGF-β signaling can activate transcription [Wotton et al. (1999) Cell 97(1): 29-39]. Signaling through the extracellular-signal-regulated kinase (ERK) increases TGIF levels [Lo et al. (2001) EMBO J 20(1-2): 128-136.]. ERK is a member of the mitogen-activate protein kinase (MAPK) pathway, which may be activated through activation of the EGF receptor pathway.
Zinc also has been shown to inhibit aggregation of platelets, particularly in a combined effect with plasma, and specifically with fibrinogen [Chvapil et al. (1975) Life Sciences (16): 561-572; Sauvage et al., U.S. Pat. No. 5,401,730].
Elastin is a resilient connective tissue protein present in the extracellular matrix and is especially abundant in tissues that undergo repeated physical deformations, i.e. lungs, blood vessels and skin [Parks (1997)]. Posttranscriptional regulation of lung elastin production. Am J Respir Cell Mol Biol 17: 1-2]. Elastin is a polymer composed of enzymatically cross-linked tropoelastin, which is the secreted soluble precursor protein [Zhang et al. (1999) Mol Cell Biol 9 (11): 7314-7326]. Similar to other structural extracellular matrix proteins, the majority of elastin production is restricted to a narrow window of development. In the majority of tissues, elastogenesis increases dramatically during late fetal life, peaks near birth and early neonatal life, decreases significantly soon after and is nearly repressed by maturity. Previous investigations have shown that insulin-like growth factor-I (IGF-I) increased elastin gene transcription through displacement of protein binding to the proximal promoter. Sp 1 and Sp3 have been identified as factors whose binding is abrogated by IGF-I [Conn et al. (1996) J Biol Chem 271(46): 28853-28860]. At the post-transcriptional level, TGF-β increases elastin gene expression through increasing the stability of tropoelastin mRNA [Kahari et al. (1992) Lab Invest 66(5): 580-588]. Zinc affects IGF-I and TGF-β expression, which suggests that zinc may increase elastin production through these two proteins. After tropoelastin synthesis, a 67 kDa elastin binding protein binds it and acts as an effective chaperone, preventing its premature intracellular aggregation [Hinek et al. (1994) J Cell Biol 126(2): 563-574]. Tropoelastin and the elastin binding protein remain bound until the complex is excreted into the extracellular space where the chaperone interacts with galactosugars of the microfibrils, decreasing its affinity for the tropoelastin molecule. Microfibrillar components act as scaffolds for the deposition of elastin. Once the tropoelastin molecules are properly aligned, they are cross-linked by lysyl oxidase [Robert (1999) Connect Tissue Res 40 (2): 75-82]. A combination of ascorbic acid, tyrosine, and zinc sulfate applied to the skin has been shown to produce a readily observable diminution of the fine wrinkle structure [Schinitsky et al., U.S. Pat. No. 4,938,969]. The mechanism was not clearly understood, but the patent states that the three ingredients were believed to function in cooperation to stimulate fibroblast proliferation and to promote their production of collagen and elastin, thereby promoting the supporting role of the associated dermal tissue (col. 2 lines 12-16).
Other patents disclose beneficial effects of certain zinc compounds when combined with other active agents on skin. Thornfeldt, U.S. Pat. No. 6,071,543 discloses combinations of salts of pyridinethiol oxides and combinations of such salts with metal oxides and thiols, to treat or prevent signs of aging in skin or mucous membranes. Specific combinations mentioned include zinc pyrithione with selenium pyrithione and zinc pyrithione with selenium sulfide. Perricone, U.S. Pat. No. 5,554,647 includes a discussion of the use of zinc (for example, in the form of zinc sulfate) as a secondary ingredient in compositions for treatment of aging skin, where the primary active ingredient in the compositions is an acetylcholine precursor. The zinc is said to be effective for enhancement of neurotransmitter synthesis. Murad, U.S. Pat. No. 5,972,999, discloses compositions for skin treatment whose primary active ingredient is one or more sugar compounds that are converted into glycosaminoglycans in the bloodstream. These compositions may also include a zinc component, preferably zinc complexed with an amino acid such as methionine. Such zinc compounds are said to assist in some way in binding collagen and elastic tissue in order to rebuild damaged or aged skin.